The present invention concerns a toaster comprising a housing containing heating means, a bread-holding carriage movable between an ejecting position to which it is returned by elastic means and a toasting position in which it is retained by an electromagnetic device. This latter comprises, on the one hand, a ferromagnetic part secured to the bread-holding carriage, and, on the other hand, an electromagnet secured to the housing. Control means act on the circuit powering the coil of said electromagnet in order to retain the bread-holding carriage during a toasting operation.
In toasters of this type, the coil of the electromagnet is supplied with current during the toasting operation in order to maintain the bread-holding carriage in a lowered position. At the end of the toasting operation, the supply of current is turned off, and the bread-holding carriage rises to the ejection position under the action of a spring.
These electromagnetic retaining devices can present problems concerning the raising of the bread-holding carriage at the end of the toasting operation. In effect, the ferromagnetic part of the bread-holding carriage retains a certain magnetization when the current in the electromagnet coil is interrupted. This magnetization, called residual magnetization, can be sufficiently strong to prevent the raising of the bread-holding carriage at the end of the toasting operation.
In order to avoid this problem, it is known to use high quality ferromagnetic material that has a weak residual magnetization, but these materials are more costly.
This problem is more serious when it is desired to obtain an electromagnetic retaining device of reduced size. In effect, in order to compensate for the decrease in the holding force of a ferromagnetic part having small dimensions, its magnetization is increased, but this leads to a stronger residual magnetization.
The invention aims to overcome these drawbacks and to provide an electromagnetic retaining device that is inexpensive and of reduced size.
According to the invention, the control means of the toaster are adapted to act on the means for interrupting the circuit for supplying power to the coil in a manner to apply a positive voltage to the coil during the toasting operation, then a negative voltage having a lower absolute value at the end of the toasting operation.
Due to this arrangement, the coil of the electromagnet creates a magnetic field that is weaker but in the opposite sense to that created during the toasting operation. This counteracts the residual magnetization of the ferromagnetic part. Thus, the attachment force of the ferromagnetic part is weaker and one obtains with certainty a return of the bread-holding carriage to the ejection position at the end of the toasting operation.